Scientists See Changes In Pugetropolis Salmon Stream Flows

The Skykomish was just a wee bit higher than I would have liked last Saturday, the final day of the season the river below High Bridge was open for steelheading.

The water had great color, but running at over 3,000 cubic feet per second at Gold Bar, the side channels I waded down in Monroe had a stouter push and deeper depth than I’d anticipated before crossing them.

Fortunately, the wading chainsamajiggers on my boots kept me from becoming river nutrients, and after a couple long hikes, the cold water that leaked into my waders warmed up.

THE SKYKOMISH NEAR GOLD BAR, ON THE LAST DAY OF WINTER STEELHEADING ON THIS STRETCH OF RIVER. (ANDY WALGAMOTT)

THE SKYKOMISH NEAR GOLD BAR, ON THE 2014-15 WINTER SEASON’S LAST DAY OF STEELHEADING ON THIS STRETCH OF RIVER. (ANDY WALGAMOTT)

No, I didn’t hook any early wild winter-runs, nor dawdling hatcheries, just a couple nontarget species.

But today I’m not here to write about the fishing or my ever-present poor luck (heck, I even left the dreaded blue cooler at home!), rather the fish and rivers.

Over the past few years I’ve become increasingly obsessed by the flows of our salmon and steelhead streams.

About this time last week I was bemoaning the mid-60-degree temps in Western Washington, especially at altitude, and the stunning lack of a snowpack on the Olympic Mountain’s Hurricane Ridge, where there are still huge patches of bare ground as of noon, Feb. 3. That doesn’t bode well for keeping creeks cool come summer.

MT. STICKNEY (LEFT) AND THE WESTERN END OF RAGGED RIDGE STAND LARGELY SNOWLESS ON JAN. 31, 2015. (ANDY WALGAMOTT)

SOUTHERN FACES OF MT. STICKNEY (LEFT) AND THE WESTERN END OF RAGGED RIDGE STAND LARGELY SNOWLESS ON JAN. 31, 2015. (ANDY WALGAMOTT)

And two Octobers ago it was that moment in September-October when the first rains perk the USGS gauge from its inexorable downward diagonal — and late in coming that season.

For that latter article, I plucked a quote from Brett Barkdull, a WDFW North Sound fisheries biologist.

“There’s been a change in summer flows,” he asserted for a 2010 story on steelhead I did. “Less water, less habitat. If a stream’s dry, it doesn’t provide much habitat for parr.”

Now, a blog by the Northwest Fisheries Science Center is directing attention to changing fall and winter flows and their importance to wild salmon.

Writes NMFS’s Michael Milstein:

Many salmon rivers around Puget Sound have experienced increasing fluctuations in flow over the past 60 years, just as climate change projections predict – and that’s unfortunate news for threatened Chinook salmon, according to a new analysis of salmon survival and river flow.

More pronounced fluctuations in flow can scour away salmon eggs and exhaust young fish, especially when lower flows force adult fish to lay eggs in more exposed areas in the center of the channel. The new study published in the peer-reviewed journal Global Change Biology says such increased flow variability has the most negative effect on salmon populations of several climate factors considered.

“There’s more flooding in late fall and winter,” said Eric Ward, an ecologist at NOAA Fisheries’ Northwest Fisheries Science Center and lead author of the research. “This is happening when the eggs are in the gravel or when the juveniles are most susceptible.”

Not all Pugetropolis streams are seeing such flow fluctuations, but 16 of 20 are (the other four have dams in headwaters), and my beloved Skykomish is one of 11 with “statistically significant increases of about 35 percent.”

It’s occurring even as the overall volume of winter runoff is staying the same, meaning, according to federal scientists, the sporadicadicity is increasing.

OK, so that’s not a word, but I think you get the gist.

So why does this matter?

To quote Milstein:

The researchers weighed several climate factors in freshwater and the ocean to determine which had the greatest effect on salmon populations. The freshwater factors included overall winter flows, peak flow timing and winter flow variability. The ocean factors included upwelling of nutrient-rich water and the Pacific Decadal Oscillation, a large-scale marine temperature pattern. Of all the factors, variation in winter river flows had the strongest influence on salmon populations, reducing their growth rate.

But wait a minute, you might say, what about humpies? We’re pit-deep in pinks every other year. How does that gel with the above equation?

“Pinks don’t spend as much time in the streams, so would tend to be less influenced by this and more by ocean conditions,” Milstein pointed out to me via email.

It can also be argued that flow pulses help salmon by reconnecting rearing habitat, putting a fresh layer of spawning gravel down,  bringing down trees for that all-important woody debris element to stream biology, and deepening those darned side channels one must wade to get to the mainstem.

But over time, there are grim implications for “depleted” stocks of anadromous fish.

“Rivers are dynamic environments, and some level of variability is to be expected in natural systems,” said Joseph Anderson, a WDFW fisheries bio and co-author of the above study, for Milstein’s story. “The point here is that as strong variability becomes more common, it eventually begins to have a negative influence on populations.”

The abstract of he and Ward’s study makes it even  more clear:

“Climate change models predict that this region will experience warmer winters and more variable flows, which may limit the ability of these populations to recover.”

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